System and method for engine control

ABSTRACT

Embodiments of the subject matter disclosed herein relate to controlling engine operating points and power for full throttle command in an off-highway vehicle, such as a diesel electric haul truck, to increase fuel efficiency. In one example, a system includes an engine and a controller. The controller is configured to determine a target engine horsepower and associated target engine speed, command the engine to operate at a first engine speed above the target engine speed, adjust a load placed on the engine to reach the target engine speed, and command the engine to operate at a second engine speed to reach the target engine horsepower.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 16/107,848, entitled “SYSTEM AND METHOD FOR ENGINECONTROL”, and filed on Aug. 21, 2018. U.S. Non-Provisional applicationSer. No. 16/107,848 is a divisional of U.S. Non-Provisional applicationSer. No. 14/856,747 entitled “SYSTEM AND METHOD FOR ENGINE CONTROL”, andfiled on Sep. 17, 2015. U.S. Non-Provisional patent application Ser. No.14/856,747 claims priority to U.S. Provisional Patent Application No.62/067,396, entitled “SYSTEM AND METHOD FOR ENGINE CONTROL”, and filedon Oct. 22, 2014. The entire contents of each of the above-listedapplications are hereby incorporated by reference for all purposes.

FIELD

Embodiments of the subject matter disclosed herein relate to controllingengine speed in a vehicle.

BACKGROUND

Historically, vehicle operators of haul vehicles (e.g., mines) wantedmaximum performance to maximize productivity of the haul vehicles.Diesel electric drive systems were tuned to extract the maximum powerout of the engine without regard to fuel efficiency. As the miningenvironment evolves, mines are becoming increasingly concerned withefficiency and are willing to accept minor impact on production.

BRIEF DESCRIPTION

In one example, a system includes an engine and a controller. Thecontroller is configured to determine a target engine horsepower andassociated target engine speed. The controller is further configured tocommand the engine to operate at a first engine speed above the targetengine speed, adjust a load placed on the engine to reach the targetengine speed, and command the engine to operate at a second engine speedto reach the target engine horsepower.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from reading the followingdescription of non-limiting embodiments, with reference to the attacheddrawings, wherein below:

FIG. 1 shows a schematic diagram of a vehicle convoy.

FIG. 2 shows a schematic diagram of a vehicle of the vehicle convoy ofFIG. 2.

FIG. 3 is a flow chart illustrating an example method for operating thevehicle of FIG. 2.

FIG. 4 is an example control diagram.

FIG. 5 is a diagram illustrating example engine parameters duringoperation of the vehicle of FIG. 2.

FIGS. 6-8 are flow charts illustrating additional example methods foroperating the vehicle of FIG. 2.

DETAILED DESCRIPTION

Embodiments of the subject matter disclosed herein relate to optimizingengine operating points and power for full throttle command in anoff-highway vehicle, such as a diesel electric haul truck. Historically,haul vehicles ran at full engine speed (e.g., 1900 rpm) and maximumpower when an operator commanded 100% throttle. According to embodimentsdisclosed herein, to reduce fuel consumption, engine speed may beinitially set to a reduced fixed speed, such as 1830 rpm, and then thedrive system may load the engine to drag the engine speed down to atarget speed, such as 1800 rpm. Additionally, the commanded engine speedmay be adjusted to allow operation at a set output (e.g., horsepower),providing significant fuel savings with minimal power reduction. Thisdisclosure adds flexibility by providing a method of respecting aspecific horsepower (HP) rather than engine speed and then determiningthe engine speed necessary to support the HP. The disclosure alsoincludes additional details on setting the desired HP level based onoperating parameters such as vehicle weight, grade (measured orestimated), and truck speed. It also describes an option of a remoteoperator (e.g., mine dispatch system) providing a max HP based onvehicle position in the haul route. It further describes a method forthe drive system to monitor operator throttle command and fine tune themax power over multiple haul cycles.

The approach described herein may be employed in a variety of enginetypes, and a variety of engine-driven systems selected with reference toapplication specific criteria. Some of these systems may be stationary,while others may be on semi-mobile or mobile platforms. Semi-mobileplatforms may be relocated between operational periods, such as mountedon flatbed trailers. Mobile platforms include self-propelled vehicles.Such vehicles can include on-road transportation vehicles, as well asmining equipment, marine vessels, rail vehicles, and other off-highwayvehicles (OHV). For clarity of illustration, a mine haul vehicle may beused as an example of a mobile platform supporting a systemincorporating an embodiment of the invention.

Before further discussion of optimizing engine operating points andpower for full throttle command, an example mine haul vehicle is shown.FIG. 1 illustrates a convoy 1 of two mine haul vehicles, each labeled“V”. While two vehicles are illustrated in FIG. 1, it is to beunderstood that any suitable number of vehicles could be included in theconvoy 1. During operation of the convoy 1, each vehicle V may beoperated to maintain a threshold distance between each vehicle and/ormaintain a threshold vehicle speed. During standard operation, eachvehicle V may be operated at full accelerator pedal command (e.g., 100%throttle), also referred to as full propel call or full call. Eachvehicle V may be controlled to a set engine speed, engine power, orother command when operated at full call. However, due to variationsbetween vehicles, full call may result in different vehicle speeds,particularly while climbing grades or when the vehicles are operatedwith large payloads. As a result, bunching of the vehicles may occur(e.g., vehicles may be forced to operate in tighter-spaced groupslimited by the slowest vehicle rather than being optimally or equallydistributed within the convoy) and/or vehicle operators may be forced toderate vehicle power.

FIG. 2 shows an example vehicle from convoy 1 including a vehicle system10. The vehicle system 10 includes a prime mover 12. In the illustratedexample the prime mover 12 is a diesel engine, and the term “engine” maybe used interchangeably with the term “prime mover” throughout theremainder of this description. The engine may include a plurality ofcylinders configured to receive fuel from a plurality of fuel injectors.The prime mover 12 drives an alternator 14. The output of the alternator14 is converted into DC via a rectifier bank 16. The DC power isprovided over a DC bus 18 to an inverter unit 20. The inverter unit 20includes DC-to-AC conversion circuitry of a known type, and also employscomponents such as Insulated Gate Bipolar Transistors (IGBTs) orthyristors operating as pulse width modulators (not shown) to provide aAC power to a traction motor 22 which is coupled to a wheel 23 through aknown type of reduction gear (not separately shown). For the sake ofillustrative simplicity, only one inverter unit 20 and traction motor 22are shown, with the understanding that the vehicle V may be providedwith multiple traction motors 22 driven by multiple inverter units 20.

While an AC-DC-AC system is described herein, is should be noted thatthe principles of the present disclosure may be applied to otherdrivetrain configurations, e.g. using an alternator or DC generator as apower source, and using AC or DC traction motors. Furthermore, theprinciples of the present disclosure are also applicable to other typesof vehicles, such as rail vehicles or road vehicles. The vehicle V mayuse any type of element adapted to exert a tractive force. Examples oftractive elements include wheels, axles, or translating or reciprocatingstructures. The term “traction motor” could encompass, for example,electric or hydraulic linear motors.

One or more chains of grid resistors 24 are connected across the DC bus18. The grid resistors 24 may be selectively coupled to the DC bus 18 todissipate power generated by the traction motor 22 and thereby providedynamic braking. This is referred to as a “retard” function. Otherelectrical energy absorbing devices may be used in place of the gridresistors 24 to dissipate and/or use the power generated, for examplebatteries, a regenerative system, or equipment to use the power likeauxiliary systems and accessories.

The vehicle V includes at least one braking device 31 of a known type.The braking device 31 may be a service, parking, or emergency brake, andmay be hydraulically, mechanically, or electrically operated. Mosttypically, the vehicle V would include a service brake system plus anemergency or parking brake system.

A microprocessor-based controller 26 has operative connections to theengine 12, the grid resistors 24, the inverter unit 20, and to numeroussensors within the drive train, such as a wheel speed sensor 28 coupledto the wheel 23. While illustrated in FIG. 2 as comprising a singleunit, it is to be understood that controller 26 may be comprised ofmultiple, separate control units that may be operatively coupled to eachother. Among other functions, the control units of controller 26 havethe capability to control the speed of the engine 12, to command theinverter unit 20 to apply current to drive the traction motor 22 in aforward or reverse direction, to modulate the current level supplied tothe traction motor 22, to control the amount of load placed on theengine 12 by the alternator 14, and to connect the traction motor 22 tothe grid resistors 24 through the inverter unit 20 to effect theretarder function. The controller 26 is provided signals from variousdiscrete sensors of the vehicle, including but not limited to signalsfrom an engine speed sensor 40 and an engine output sensor 42. Inaddition to the various discrete sensors, the controller 26 is providedwith feedback from the inverter unit 20 which is indicative of themagnitude of the torque being applied to the traction motor 22. Thecontroller 26 is also provided with a mechanism for determining theweight of a payload carried by the vehicle V, such as via a suspensionpressure calculation. For example, the vehicle V may include a payloadmeter 33 which computes total vehicle weight based on sensed airpressure in the vehicle's suspension struts 35. The payload meter 33 cancommunicate the total vehicle weight to the controller 26 over acommunications channel such as a serial bus. The payload may bedetermined in another suitable manner, such as provided to thecontroller from an off-board sensor.

A control panel 30, also referred to as a “driver information display”is coupled to the controller 26. The control panel 30 includes a displayfor presenting information to the driver, and one or more controls foroperating the vehicle V. In some examples the display is a multi-lineLED, and the controls are configured as a plurality of fixed andconfigurable keys. It will be understood that the control panel could beconfigured differently, for example it could take the form of a touchscreen interface. In addition to the control panel 30 the vehicle V alsoincludes one or more discrete vehicle controls operatively coupled tothe controller 26, such as accelerator pedal (not shown).

Optionally, the controller 26 may include means for two-waycommunication with a remote operator or dispatcher (see FIG. 1, shownschematically at 38). As illustrated the controller 26 is coupled to atransceiver 36 which communicates with the dispatcher 38 through awireless link.

The controller 26 may include non-transitory instructions executable tocarry out one or more methods described herein. As explained above,controller 26 may be comprised of multiple control units operativelyconnected to one another. For example, a first control unit may regulatefueling of the engine and a second control unit may regulate load placedon the engine by the alternator. The first control unit may regulatefueling of the engine by sending a signal to adjust an opening degreeand/or duration of one or more fuel injectors of the engine (e.g., thesignal may cause a solenoid in the fuel injector to be energized for agiven duration to open the fuel injector). The second control unit mayregulate load placed on the engine may adjusting the electrical load onthe alternator, which is proportional to the load placed on the engineby the alternator. To adjust the electrical load on the alternator, thesecond control unit may selectively couple the alternator to theresistive grids, increase output of the traction motors, etc.Additionally, the second control unit may send an engine speed commandto the first control unit.

As explained previously, to reduce fuel consumption, a vehicle having adrive system, such as the vehicle V described above with respect to FIG.2, may be operated at a set engine horsepower when a maximum throttlerequest is received. The set engine horsepower may be based on operatingparameters, predetermined in advance based on capabilities of thevehicle, or other suitable parameters. To achieve operation at the sethorsepower, once a maximum throttle request is received and the sethorsepower determined, a target engine speed is obtained, for examplefrom a look-up table, based on the set horsepower. The target enginespeed is used as input to the fuel controller (e.g., the first controlunit described above), and fuel amounts supplied to the engine may beadjusted to reach the target engine speed. During the period of timewhere engine speed is increasing from the initial speed to the targetspeed, engine horsepower may be unregulated. Once the target enginespeed is reached (or once an engine fueling limit is reached), the drivesystem controller (e.g., the second control unit described above) mayadjust the load placed on the engine by the alternator until the sethorsepower is reached. In this way, the engine may be operated at anoperating point for maximum torque and hence highest efficiency, and theengine speed maintained at a lowest possible speed for the desiredoutput.

Turning now to FIG. 3, a method 300 for operating an engine at a targethorsepower is presented. Method 300 may be performed by a controller,such as the controller 26 described above, in combination with varioussensors and actuators, such as an engine speed sensor, engine outputsensor, fuel injectors, etc., according to instructions stored on memoryof the controller. In one example, method 300 is performed by the secondcontrol unit of controller 26, described above, that controls drivesystem (e.g. controls the load placed on the engine by the alternator).At 302, method 300 includes receiving a propel call request. The propelcall request may include an operator of the vehicle depressing anaccelerator pedal, for example, or other input mechanism requesting agiven vehicle speed. At 304, method 300 determines if the requestincludes a full propel call request. A full propel call request mayinclude a fully depressed accelerator pedal, a 100% throttle request, orother maximum vehicle speed request. If a full call request is notreceived, method 300 proceeds to 324 to send an engine speed command toa separate fuel control unit (e.g., the first control unit describedabove) and adjust the load placed on the engine to reach a targethorsepower defined by the requested propel call. The fuel control unitmay adjust engine fueling to reach the commanded speed. Method 300 thenends.

If a full call request is received, method 300 proceeds to 306 todetermine a target horsepower (HP). The target HP may be determinedaccording to a suitable mechanism. In one example, the target HP may bea target predetermined during a previous operation, or may be a targetpredetermined by a user, such as an operator of the vehicle or a remoteoperator in communication with the vehicle. The target HP may be themaximum HP the engine is capable of providing. In another example, thetarget HP may be a default HP, such as 90% of peak configured HP.Further, the target HP may be adjusted based on operating conditions.For example, the default target HP described above may be adjusted basedon vehicle weight, as indicated at 308. As vehicle weight increases, thetarget HP may increase to allow the vehicle to maintain a desiredvehicle speed. In another example, the default target HP may be adjustedbased on the grade at which the vehicle is traveling, as indicated at310. This may include increasing the target HP as grade increases. In afurther example, the default target HP may be adjusted based on vehiclespeed, as indicated at 312. This may include increasing the target HP asvehicle speed increases. Additionally, in some examples, the defaulttarget HP may be adjusted based on user input, as indicated at 314.Further, the target HP may be within a range of 60-100% of maximum ratedHP for the vehicle.

At 316, a rated engine speed is determined based on the target HP. Inone example, the rated engine speed may be obtained from a look-up tablethat is indexed to the target HP, or according to another suitablemechanism. The rated engine speed may be an engine speed thatcorresponds to maximum torque for the engine, for example, in order tooperate the engine at high efficiency. In an example, the control unitmay be configured to adjust the look-up table that indexes rated enginespeed to target HP based on past engine operation. For example, onceoperation at maximum torque is achieved, if one or more of the enginespeed or HP achieved at the maximum torque deviates from the values inthe table, the table may be adjusted. At 318, a first engine speedcommand is sent to the separate fuel control unit. The first enginespeed command may be the rated engine speed determined above in oneexample. In another example, the first engine speed may be an enginespeed that is slightly above the rated engine speed, such as between1-5% above the rated engine speed or a set speed above the rated enginespeed, such as 30 rpm above the rated engine speed. In this way, theseparate fuel control unit may adjusting fueling to the engine toattempt to reach the first engine speed command.

At 320, the load placed on the engine is adjusted to reach the ratedengine speed. The load may be placed on the engine by the alternator,and thus alternator load may be adjusted (e.g., electrical loads on thealternator coupled or uncoupled or other suitable mechanism) to adjustthe engine load. The load placed on the engine may be adjustedconcurrent to the fueling adjustment performed by the fuel control unitto reach the rated engine speed. If the first engine speed command islarger than the rated engine speed, the load placed on the engine by thealternator acts to drag engine speed down from the commanded enginespeed. In doing so, the engine may be operated at its maximum torqueline for a given engine speed, achieving higher efficiency. Further, therated engine speed may be a lower speed than the maximum rated speed,thus enabling a reduction in fuel consumption.

As explained above, the load placed on the engine acts to drag theengine speed down to the rated speed. During this time, horsepower maybe relatively unregulated (e.g., not held to a specific horsepower).Once the rated engine speed is reached, the speed command sent to thefuel control unit may be adjusted to bring the engine horsepower to thetarget horsepower. Thus, at 322, method 300 includes adjusting theengine speed command to a second engine speed command and adjusting theload placed on the engine to reach the target horsepower. The enginespeed command may be adjusted based on the difference between the actualhorsepower and the target horsepower in one example, or according toanother suitable mechanism. Method 300 then ends.

When the load placed on the engine drags the engine speed down, theamount of fuel supplied to the engine may continue to increase as theload is applied to the engine as the fuel control unit attempts to reachthe commanded engine speed. However, the amount of fuel supplied to theengine may be limited by various parameters, such as peak cylinderpressure, air-fuel ratio limit, or other parameters, such that theengine operates with a maximum amount of fuel for highest efficiencywhile the alternator maintains the engine speed at a lowest possiblespeed for maintaining the target horsepower.

Thus, according to the method of FIG. 3, the engine speed is adjusted toreach the targeted HP at the most efficient operating point of theengine, which may be when the engine is on the max torque curve. In someexamples, the method may slowly increase or reduce engine speed whilecontinuing to fully load the engine at that speed. The method may beimplemented according to a control scheme with an outer control looptrying to reach a specific HP set point adjusting the engine speedsetpoint and an inner loop adjusting the HP load applied to the engineto hold engine speed to the setpoint.

FIG. 4 is a diagram 400 illustrating an example control routine foradjusting an engine to operate at a target horsepower. In one example,the control routine of diagram 400 may be enacted during a full propelcall (e.g., when a throttle is set at maximum). The control routine ofdiagram 400 may represent the inputs, outputs, and actions taken by thecontroller during the execution of method 300 of FIG. 3, describedabove. As described previously and in more detail below, the controllermay be comprised of separate control units, including a first controlunit for regulating fuel to the engine and a second control unit forregulating the load placed on the engine by the drive system.

As shown in diagram 400, in a first loop of the control diagram, atarget horsepower obtained in a suitable manner (e.g., from a remotedispatch, based on operating parameters, etc.) is entered into a look-uptable 402 in order to obtain a target or rated engine speed. The targetengine speed is input to offset block 404, which adds an offset (e.g.,30 rpm) to the target engine speed to produce an engine speed commandthat is entered into a first control block 406 (which may located on thefuel control unit) to determine a fuel amount to supply to the engine.The fuel amount may represent the amount of fuel that is to be suppliedby each fuel injector of the engine, or it may represent a total amountof fuel to be supplied per engine cycle, for example. The amount of fuelis supplied to the engine (represented by block 408). As the engineoperates, engine speed (RPM) and output (HP) are measured by therespective sensors.

In a second loop of the control diagram, the target horsepower iscompared to the measured horsepower at a load error block 410. Thedifference between the target and measured horsepower is input into aspeed control block 414 along with the target engine speed to determinean adjustment to the speed command. The adjusted speed command (e.g.,second engine speed command described above with respect to FIG. 3)comprises the speed that the drive system control unit loads the enginedown to reach. In some examples, the speed control block 414 maymaintain the commanded engine speed at the first speed until measuredengine horsepower exceeds the target horsepower, at which time theengine speed command may be adjusted (e.g., lowered). The adjustedengine speed command is also input into a speed error block 416 todetermine the difference between the adjusted speed command and actualengine speed. This error is input into a second control block 412 alongwith the error determined at block 410. Based on the difference betweenthe target and measured horsepower as well as the difference betweenmeasured engine speed and the adjusted engine speed command, the secondcontrol block determines an amount of load to place on the engine by thealternator. For example, if the measured horsepower is less than thetarget horsepower, additional load may be placed on the engine by thealternator.

As explained above, the first control block 406 may be located on thefuel control unit while the second control block 412, along with the maplook-up, offset block 404, speed adjustment block 414, load error block,and speed error block 416, may be located on the drive system controlunit.

FIG. 5 is a diagram 500 illustrating example operating parameters duringexecution of the control routine of FIG. 4 and/or the method of FIG. 3.Diagram 500 illustrates a fuel amount supplied to engine, represented bycurve 502, engine speed, represented by curve 504, and engine output(HP), represented by curve 506. For each operating parameter, time isdepicted along the x-axis and respective values for each parameter isdepicted along the y-axis.

Prior to time t1, the vehicle may be operating at a steady,less-than-full propel call. For example, the vehicle may be traveling ona flat surface prior to reaching a grade out of a mine quarry.Accordingly, the engine is operating at less than maximum fueling,engine speed, and load. At time t1, an operator may request a fullpropel call (e.g., maximum throttle) in response to starting to ascend asteep grade out of the quarry, for example. In order to reach the targethorsepower set for full call, the amount of fuel supplied to the engineincreases in order to increase engine speed. Engine horsepower alsobegins to increase. At time t2, engine speed reaches the target speed,which may include an offset such that the target engine speed isactually higher than a desired engine speed. Accordingly, the horsepowercontinues to increase to drag the engine speed down to a lower, secondtarget engine speed (e.g., the target engine speed minus the offset). Asthis second engine speed is also commanded to the fuel control unit asthe target engine speed at time t2, the horsepower of the engine alsodecreases to the target horsepower. Due to the reduction in engine speed(while maintaining operation at full target horsepower), the amount offuel that is supplied to the engine decreases, thus resulting indecreased fuel consumption. The method, control diagram, andcorresponding operating parameters described above with respect to FIGS.3-5 disclosed an example of reaching a target horsepower in response toa request to operate at maximum engine output (e.g., a full propel callor maximum throttle request). However, the mechanism of reaching atarget horsepower may be applied during other operating conditions, suchwhen full call is not requested but the requested engine output isrelatively close to full call, such as >80% maximum output. For example,if a first vehicle is climbing a hill and reaches a threshold distancefrom a second vehicle traveling in front of the first vehicle, theoperator of the first vehicle may reduce engine output to avoid hittingor otherwise traveling too close to the second vehicle. In such anexample, the target horsepower for the first vehicle may be reduced andthe new target horsepower reached according to the method describedabove. Further, if the operator of the first vehicle subsequentlyreturned to full propel call, the same mechanism could be used to reachthe full target horsepower.

In another example, the method for reaching the target horsepowerdescribed above may be used during an acceleration event that may notnecessarily include a request to operate a full propel call. Further, insome examples it may be desirable to slow down the rate of the increasein engine speed when attempting to reach the target horsepower inresponse to a request to operate at maximum engine output, in order toreduce fuel consumption during the acceleration. FIG. 6 illustrates amethod 600 for operating an engine during an acceleration event. Similarto method 300, method 600 may be performed by a controller, such as thecontroller 26 described above, in combination with various sensors andactuators, such as an engine speed sensor, engine output sensor, fuelinjectors, etc., according to instructions stored on memory of thecontroller.

At 602, method 600 includes receiving a propel call request, e.g., apower setting requested by an operator of the vehicle. At 604, method600 determines if the request includes an acceleration event, forexample if the request includes an increase in requested power. If no,method 600 proceeds to 606 to maintain current operating parameters,which may include maintaining current engine speed and/or horsepower, orto initiate a deceleration. Method 600 then returns.

If an acceleration event is requested, method 600 proceeds to 608 todetermine a first target horsepower. The first target horsepower may bedetermined in a similar manner as the target horsepower described abovewith respect to FIG. 3. However, the first target horsepower may be adifferent horsepower than the target horsepower that is desired for therequested propel call in order to increase or decrease the rate of theacceleration.

At 610, a target engine acceleration rate may be determined based on thetarget horsepower, for example from a look-up table. At 612, an enginespeed command is sent from the drive system control unit to the fuelcontrol unit in order to reach the target acceleration rate. Further, at614, the load placed on the engine by the alternator may be adjusted toreach the first target horsepower.

At 616, it is determined if the first acceleration rate is reached. Ifnot, method 600 loops back to 614 to continue to adjust the loading ofthe engine until the target rate is reached. Once the target rate isreached, method 600 proceeds to 618 to adjust the load placed on theengine to reach a second target horsepower. The second target horsepowermay be different than the first target horsepower, for example it may belower. In this way, the engine may be rapidly accelerated until adesired acceleration rate is achieved, and then the target horsepowermay be lowered to maintain the target acceleration rate. Further, insome examples, once a target engine speed has been reached, the loadingon the engine may be adjusted to reach a third target horsepower, whichmay be the same as the second target horsepower, or it may be different.

Off-highway vehicles, such as mine haul vehicles, may be operated in aconvoy over cycles that include a trip from a loading site to a dumpsite and back, for example. These mine haul cycles are typically limitedby the slowest vehicle configuration within the convoy. A lower power togross vehicle weight (GVW) haul truck can limit on-grade speed for amuch faster haulage class configuration. A single slow truck with low HPor overloaded of identical haulage configuration can also slow on gradespeeds. In these scenarios, where convoy includes vehicles with mixedconfigurations, a mine may benefit from simple HP/ton GVW matching.

Thus, according to embodiments disclosed herein, optimization for fuelis achieved for vehicles operating in a convoy with a slower vehicle. Instandard state of the art system, the operator in the faster vehiclewill decrease accelerator request to maintain the speed of slowervehicle. However, as disclosed herein, reduced HP demand is identifiedto allow a vehicle to operate at optimal efficiency for the less thanpeak performance points. In mines with mixed fleets, it may be desirableto reduce HP on vehicles to improve fuel, which essentially keeps thevehicles with a balanced HP per ton GVW.

FIG. 7 illustrates a method 700 for limiting target HP based on a slowvehicle. The method of FIG. 7 may address the issues described above byautomatically limiting the HP of a vehicle when it is detected that thevehicles has been operated at a reduced load call for a given amount oftime. Method 700 may be carried out by a controller, such as controller26 of FIG. 2, according to instructions stored on memory of thecontroller, similar to the methods 300 and 600 described above.

At 702, method 700 includes determining operating conditions. Theoperating conditions may include current load call, time spent atcurrent load call, and other parameters. At 704, method 700 includesdetermining if a load call reduction request has been received. Forexample, a vehicle operator may reduce an accelerator request. In someexamples, only a change of load call greater than a threshold may bedetected, such as a reduction to 80% or 90% load or a change of 3% orgreater from full call. If no reduction has been requested, method 700proceeds to 706 to maintain current operating parameters, and thenmethod 700 ends. If a reduction has been requested, method 700 proceedsto 708 to determine if the reduction request has been sustained for athreshold duration, such as 30 seconds. If no, method 700 proceeds to706 and then ends.

If yes, method 700 proceeds to 710 to reduce the peak HP limit. The peakHP limit may be set at a percentage of the target HP determinedaccording to the method of FIG. 3, for example. In the example describedabove, a 90% call may result in a reduced HP limit of 90% of the targetHP. However, the HP limit may be reduced according to any suitablemechanism. The reduced HP limit may be maintained, even after theoperator returns to the accelerator to the full call position, asindicated at 712. A Diagnostic Information Display (DID) can be used tohave a tab with what HP limit is being applied, so that if there isquestion if this limit is being applied it can be displayed in real timeto operator.

To release the reduced HP limit, method 700 determines if theaccelerator has been released to or past the original reduced load callat 714. If no, method 700 returns to 712 to continue to operate with thereduced peak HP limit. If yes, method 700 proceeds to 716 to release thereduced HP limit and return to the target HP limit. In another example,if the vehicle has been operated at full call for greater than athreshold period of time, the reduced peak HP limit may be lifted. Insome examples, rather than release the HP limit suddenly resulting in arapid increase to full call, the limit may be released gradually. Method700 then ends.

Thus, method 700 provides for imposing a reduced HP limit once a loadreduction request has been sustained. For example, after 0.5 minute ofstable decreased performance operation the system reduces peak HPcapability to allow an operator to maintain the reduced performancespeed at a full pedal request.

Full HP can be requested by the operator releasing the accelerator pedalto the previous level or less than the previous level that prompted thereduced performance. In the 90% call example the operator could let offthe pedal to 90% and speed on grade would not change, but re-applicationwould allow 100% full HP again.

This reduced peak HP limit feature described above may be utilized toidentify a mine that is running a mixed fleet and would benefitsignificantly by having a reduced HP on the faster vehicles. This shouldeliminate the need for mine to be adjusting each vehicle to specific HPto match haul speeds of various vehicles.

To facilitate this analysis, the following inputs may be used: enable HPreduction feature, HP Δ per haul cycle, time at reduced HP on grade totrigger HP change for next cycle, time at full propel call on grade totrigger HP change for next cycle, and minimum % call to enable thefeature (default 70%). By analyzing this information over one or morehaul cycles, it may be determined that a vehicle is operating atless-than-full call a significant amount of time, and its peak HP limitmay be reduced, not just transiently but permanently, until furtheranalysis reveals the vehicle is once again operating at full call amajority of the time, at which time the peak HP limit may be increased.When operating with a reduced peak HP limit, a Diagnostic InformationDisplay (DID) can be used to have a tab with what HP limit is beingapplied (or another output mechanism may be activated, such as anindicator light), so that if there is question if this limit is beingapplied it can be displayed in real time to the operator.

FIG. 8 illustrates a method 800 for a smart maximum HP limit over a longcycle is presented. At 802, method 800 includes initiating a monitor atthe start of a first haul cycle. The monitor may collect the informationdescribed above, including collecting an amount of time above athreshold % call (e.g., 70%) at 804, to remove time spent at idle,stopped, etc., from the analysis. This may include, in some examples,collecting the amount of time spent on a grade, which may be determinedby evaluating torque applied by the wheel motors or speed and power, ormay be determined by measuring incline with a sensor. At 806, theproportion of time spent at full call is determined. In some examples,this may include determining the proportion of time spent at full callwhile operating on a grade (e.g., a grade of greater than 0%). At 808,method 800 determines if the percent time at full call is less than asecond threshold. The second threshold may be a suitable threshold thatindicates the vehicle desired power may be limited by another vehicle inthe convoy, such as 90%, 80%, or other suitable threshold. If thepercent at full call is not less than the second threshold, method 800proceeds to 810 to maintain a current peak HP limit, and then method 800returns. If the percent at full call is less than the second threshold,method 800 proceeds to 812 to reduce the peak HP limit by a ΔHP/cycle onthe next haul cycle. The ΔHP/cycle may be a fixed value (e.g., 5%), orit may represent the average change in HP over the current and/orprevious haul cycles.

At 814, the monitor is initiated at the start of the next haul cycle.The monitor collects the time at the percent call above the firstthreshold at 816 and determines the percent at full call at 818. At 820,method 800 determines if the percent at full call is less than thesecond threshold. If yes, method 800 proceeds to 822 to reduce the peakHP limit by ΔHP/cycle on the next cycle, and then method 800 returns.However, if the answer at 820 is no, method 800 proceeds to 824 todetermine if the percent at full call is greater than a third threshold,higher than the second threshold. If the answer is no, method 800proceeds to 810 to maintain current operating parameters. If the answeris yes, method 800 proceeds to 826 to increase the peak HP limit byΔHP/cycle on the next cycle, and then method 800 returns.

Thus, according to method 800, for each cycle the propel call (whileabove a minimum percentage propel call) is collected. If the vehiclespends a significant amount of time below full propel call, the systemwill remove HP from the system limit using the HP Δ per haul parameter.If the next cycle has a long period of time at the 100% (indicatesincreased HP could be utilized) the next cycle will be increased by theHP Δ. The increase function is needed because if all vehicles have acontinually reducing HP feature and no way to increase it automaticallythen natural load variation could cause such a feature to continuallyreduce fleet HP, which may not be desirable. In some examples, theamount of HP that can be removed by this feature may be limited by apredetermined bound, for example up to 10%. Further, in some examples,the Δ hp/cycle may be obtained from a look-up table based on the averagepropel call percent (e.g., a lower average propel call percent causes alarger adjustment after that cycle).

Thus, the methods and systems described above provide for multiplemechanisms for adjusting engine speed and/or power output of anoff-highway vehicle. In one example, an adjustable HP target may beused, and a target engine speed determined based on the target HP. Thetarget engine speed may be adjusted to include an offset such that theengine is commanded to operate a higher engine speed than the target,and the engine may be loaded to drag engine speed down to the targetspeed. Further, once the target engine speed is reached, if the engineis not operating at the target HP, the engine speed commanded to theengine may be adjusted until the engine output reaches the target HP.This feature may reduce rated speed in a continuous fashion to theminimum needed to make rated power, while providing closed loop ontraction power. The engine speed setpoint may be moved up or down tomake desired traction HP.

Further, a smart maximum HP limit is provided. When on grade, thepercentage of time not at full power is monitored. If this exceeds athreshold, the HP is reduced, resulting in reduced speed on grade andrunning at new “rated” point. To optimize operating point, advanced maxHP logic may be included.

An embodiment for a system is provided. The system includes an engine;and a controller configured to: determine a target engine horsepower andassociated target engine speed; command the engine to operate at a firstengine speed above the target engine speed; and adjust a load placed onthe engine to reach the target engine speed. The controller may befurther configured to command the engine to operate at a second enginespeed to reach the target engine horsepower. The controller may beconfigured to adjust the load placed on the engine to reach the targetengine speed, up to a maximum load. The controller may be configured tocommand the engine to reduce engine speed if engine horsepower is abovethe target engine horsepower while the load is placed on the engine. Tocommand the engine to operate at the first engine speed, the controllermay be configured to send a command to operate at the first engine speedto a separate fuel controller. The controller may be configured toadjust the load placed on the engine to reduce engine speed from thefirst engine speed to the second engine speed, the second engine speed alowest possible engine speed that maintains the target enginehorsepower. The controller may be configured to select the target enginespeed based on one or more of the target engine horsepower and maximumtorque. The controller is configured to select the target enginehorsepower based on operating conditions. The controller may beconfigured to determine the target engine horsepower and command theengine to operate at the second engine speed to reach the target enginehorsepower in response to receiving a full throttle request. Thecontroller may be configured to, if a less than full throttle request isreceived, determine a second target engine horsepower and associatedsecond target engine speed, command the engine to operate at a thirdengine speed above the second target engine speed, and adjust the loadplaced on the engine to reach the second target engine speed. Thecontroller may be further configured to monitor an amount of time spentoperating under the full throttle request over one or more operatingcycles, and if the amount of time is less than a threshold, thecontroller is configured to lower the target engine horsepower for asubsequent operating cycle. In some examples, the target enginehorsepower is lowered by a predetermined amount. In other examples, thetarget engine horsepower is lowered by an amount based on the time spentoperating under the full throttle request. The system further comprisesone or more traction motors and an alternator, the alternator driven bythe engine to generate electrical power to drive the one or moretraction motors, and wherein the load placed on the engine to reach thetarget engine horsepower is load placed on the engine by the alternator.

Another embodiment for a system for a vehicle comprises an engine havinga plurality of cylinders; a fuel system to supply fuel to the engine; adrive system including an alternator to provide electrical energy to aplurality of traction motors, the alternator driven by the engine; and adrive system controller configured to send a command operable to controlthe fuel system to supply an amount of fuel to the engine based on atarget engine speed and control the drive system to adjust a load placedon the engine and engine speed to reach a target engine horsepower.

The drive system controller is configured to adjust the load placed onthe engine and the engine speed by placing a load on the engine from thealternator. The target engine speed may comprise an engine speed that isgreater than a selected engine speed that is selected based on thetarget engine horsepower. In one example, the target engine horsepoweris received from a remote dispatch system.

An embodiment relates to a method, comprising: responsive to receiving arequest to increase engine power, adjusting an engine speed command toreach a target engine acceleration rate, and adjusting a load placed onthe engine based on a first target horsepower; and once the targetengine acceleration rate is reached, adjusting the load placed on theengine based on a different, second target horsepower.

In an example, the second target horsepower is lower than the firsttarget horsepower. The method further comprises determining a targetengine speed based on the second target horsepower, and adjusting theengine speed command to reach the target engine speed. Adjusting theengine speed command may comprise adjusting an engine speed command sentto a remote engine fuel controller, and adjusting the load placed on theengine may comprise adjusting a load placed on the engine by analternator.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Moreover, unlessexplicitly stated to the contrary, embodiments “comprising,”“including,” or “having” an element or a plurality of elements having aparticular property may include additional such elements not having thatproperty. The terms “including” and “in which” are used as theplain-language equivalents of the respective terms “comprising” and“wherein.” Moreover, the terms “first,” “second,” and “third,” etc. areused merely as labels, and are not intended to impose numericalrequirements or a particular positional order on their objects.

This written description uses examples to disclose the invention,including the best mode, and also to enable a person of ordinary skillin the relevant art to practice the invention, including making andusing any devices or systems and performing any incorporated methods.The patentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those of ordinary skill in the art.Such other examples are intended to be within the scope of the claims ifthey have structural elements that do not differ from the literallanguage of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal language of theclaims.

The invention claimed is:
 1. A method for operating an engine,comprising: responsive to receiving a request to increase engine power,determining a first target horsepower and a target acceleration ratebased on the target horsepower; adjusting an engine speed command toreach a target engine acceleration rate; adjusting a load placed on theengine based to reach the first target horsepower; and once the targetengine acceleration rate is reached, further adjusting the load placedon the engine.
 2. The method of claim 1 wherein once the target engineacceleration rate is reached, the load placed on the engine is adjustedbased on a different, second target horsepower.
 3. The method of claim 1wherein the engine is in a vehicle, the vehicle being a mine haulvehicle.
 4. The method of claim 3 further comprising operating thevehicle in a convoy.
 5. The method of claim 4 further comprisingresponsive to receiving a request to decelerate the vehicle, including areduced HP demand, reducing a peak horsepower limit.
 6. The method ofclaim 4 wherein the reduced peak horsepower limit is determined as apercentage of one of the first and second target horsepowers.
 7. Amethod, comprising: operating a convoy of mine haul vehicles, where afirst vehicle in the convoy has a lower power to gross vehicle weight(GVW) than a second vehicle in the convoy and matching HP/ton GVW of thevehicles by limiting a peak HP limit of the second vehicle responsive toa request to decelerate the second vehicle.
 8. The method of claim 7further comprising automatically limiting the HP of the second vehiclewhen it is detected that the vehicle has been operated at a reduced loadcall for a given duration.
 9. The method of claim 8 whereinautomatically limiting the HP of the second vehicle includes setting thepeak HP limit of the second vehicle at a percentage of a target HP. 10.The method of claim 8 wherein automatically limiting the HP of thesecond vehicle includes monitoring parameters over one or more haulcycles, and determining that a vehicle is operating at less-than-fullcall a threshold amount of time, and limiting the vehicle's peak HPlimit responsive thereto.
 11. The method of claim 10 wherein theoperating parameters comprise one or more of an enable HP reductionfeature, a HP Δ per haul cycle, a time at reduced HP on grade to triggerHP change for next cycle, a time at full propel call on grade to triggerHP change for next cycle, and a minimum % call to enable the feature.12. The method of claim 10 wherein the limiting includes limiting HPuntil further analysis reveals the vehicle is once again operating atfull call more than the threshold duration, at which point the peak HPlimit is increased.
 13. The method of claim 12 wherein the analysisignores idle operation.
 14. The method of claim 10 further comprising,when operating with a reduced peak HP limit, operating with a DiagnosticInformation Display (DID) providing a display to an operator with whatHP limit is being applied.
 15. The method of claim 8 wherein anadjustable HP target for each vehicle is used, and a target engine speeddetermined based on the target HP.